This invention relates to the conversion of C.sub.12 -C.sub.19 alkyladamantane hydrocarbons in which the alkyl groups are of the C.sub.1 -C.sub.3 range and/or their corresponding monools to compounds having two linked adamantane nuclei per molecule. For convenience, these linked compounds are herein referred to as "bistype" products. They include hydrocarbon products in which the adamantane nuclei are coupled to each other solely through an alkylene linkage and also certain oxygen-containing products wherein the nuclei are joined not only through a methylene or ethylene linkage but also through an ether linkage.
The adamantane nucleus has ten carbon atoms, four of which are bridgehead carbons that are equivalent to each other, as can be seen from the following typographical representation: ##STR1## As shown, the bridgehead carbon atoms customarily are designated by the numerals 1, 3, 5 and 7 respectively, and these bridgehead positions are all equivalent to each other in the nuclear structure.
Starting materials for the present process are alkyladamantanes and/or alkyladamantanols of the C.sub.12 -C.sub.19 range. The starting reactant can have one, two or three alkyl substituents on the adamantane nucleus, such substituents being of the C.sub.1 -C.sub.3 range. In other words, the alkyl substituents can be methyl, ethyl, n-propyl or isopropyl. Methods of preparing these feed materials are known in the prior art.
The preparation of methyl- and/or ethyl-substituted adamantanes by the isomerization of tricyclic naphthenes by means of an aluminum halide or HF-BF.sub.3 catalyst has been described by several references including the following: Schneider U.S. Pat. No. 3,128,316, dated Apr. 7, 1964; Janoski and Moore U.S. Pat. No. 3,275,700, dated Sept. 27, 1966; Schneider et al. U.S. Pat. Nos. 3,336,405 and 3,336,406, dated Aug. 15, 1967; Schneider U.S. Pat. No. 3,356,751, dated Dec. 5, 1967; Schleyer et al., Tetrahedron Letters No. 9, pps. 305-309 (1961); and Schneider et al., JACS, 86, pps. 5365-5367 (1964). The isomerization products can have the methyl and/or ethyl groups attached to the adamantane nucleus at either bridgehead or nonbridgehead positions or both, although completion of the isomerization reaction favors bridgehead substitution. Examples of alkyladamantanes made by such isomerization are dimethyladamantanes, ethyladamantanes, methylethyladamantanes, dimethylethyladamantanes and trimethyladamantanes.
Preparations of adamantane hydrocarbons having C.sub.3 or higher alkyl substituents have been described in the following references: Schneider U.S. Pat. No. 3,382,288, dated May 7, 1968; and Spengler, et al., Erdol und Kohle-Erdgas-Petrochemie, Vol. 15, pp. 702-707 (1962).
Procedures for converting adamantane hydrocarbons to bridgehead hydroxy derivatives have been described in the prior art. Schneider U.S. Pat. No. 3,356,740, dated Dec. 5, 1967, discloses the conversion of alkyladamantanes to bridgehead alcohols by air oxidation using a soluble metallic organic salt as catalyst, as also does Schneider U.S. Pat. No. 3,450,775, dated June 17, 1969. Moore U.S. Pat. No. 3,383,424, dated May 14, 1968, shows the oxidation of alkyladamantanes by means of chromic acid in aqueous acetic acid under conditions to produce either monools or diols.
The preparation of nonbridgehead adamantanols containing nonbridgehead alkyl groups from adamantanone and their conversion to the corresponding nonbridgehead alkyladamantanes have been described by Landa et al., Collection Czechoslov. Chem. Commun.,/Vol. 32/(1967).
Alkyladamantanols in which the hydroxy group is at a nonbridgehead position can be made similarly from keto derivatives of alkyladamatanes which are obtained as by-products of the air oxidation process disclosed in aforesaid Schneider U.S. Pat. No. 3,356,740. Conversion of the keto group can be carried out by a Grignard synthesis in the manner described in the aforesaid Landa et al. reference or by Schleyer et al., JACS, 83, 186, which shows the reaction of adamantanone with methyl iodide and magnesium to yield 2-methyladamantanol-2. In analogous fashion the keto by-products of U.S. Pat. No. 3,356,740 can be converted to nonbridgehead alkyladamantanols also having at the nonbridgehead position an ethyl, n-propyl or isopropyl substituent in addition to the alkyl substituents that were present in the starting alkyladamantane hydrocarbon.
In the prior art, the preparation of two bis-type adamantane hydrocarbons having an ethylene linkage between the nuclei has been described by Stepanov and Baklan, J. GEN. CHEM. USSR, Vol. 34(2), pages 580-584 (1964). Specifically, these compounds were 1,2-bis(adamantyl-1)-ethane and 1,2-bis(1-methyladamantyl-3)-ethane, both being high melting solids having melting points, respectively, of 289.degree. C. and 153.degree. C. They were made from 1-hydroxymethyladamantane by classical synthesis techniques involving Grignard reactions, the reaction routes being entirely different from reactions which occur in the process of the present invention.
Reinhardt U.S. Pat. No. 3,342,880, dated Sept. 19, 1967, discloses the coupling of adamantylamide molecules together through a methylene linkage by a reaction also quite different from reactions of the present process. Specifically, this coupling was effected by reaction of the adamantylamide with formaldehyde in the presence of strong sulfuric acid, and the resulting methylene linkage was attached to each of the coupled adamantane nuclei at a bridgehead position.